Analyst: Intel Reverse-Engineered AMD64

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After investigating the instruction sets used by 64-bit chips from AMD and Intel, an industry analyst has concluded that Intel reverse-engineered the AMD64 instruction set to create its own 64-bit microprocessor architecture.

Tom Halfhill, an analyst at In-Stat/MDR in San Jose, said Monday that he had compared the instruction sets of AMD’s 64-bit chips, called AMD64, with the 64-bit extensions to be used in the Intel Xeon processor and future desktop chips. The smoking gun, Halfhill said, was Intel’s choice to mimic a decision AMD made in its early Opteron designs, and later reversed.

Speculation that Intel had reverse-engineered AMD’s processor began circulating almost immediately after Intel announced its own 64-bit plans in February. AMD announced plans to develop its 64-bit Opteron processor, then code-named “Hammer”, in Oct. 2001, and began shipping it in April 2003. Intel’s “Nocona”, the first chip to use its own 64-bit extensions, will launch this quarter with the Intel Extended Memory 64 Technology, or “Intel EM64T”.

While exactly copying a processor’s microarchitecture would be illegal, creating a compatible product through the use of an original “clean room” design is legally protected. According to Halfhill, Intel clearly reverse-engineered AMD’s products, a tactic AMD and other X86 chip designers have used to quickly catch up to Intel’s historical leadership in the design of new microprocessors.

Intel’s decision, however, clearly places AMD in the role of market leader. “There’s no shame in it,” Halfhill said of the reverse-engineering. “AMD has reverse-engineered everything Intel has done for years.”

Halfhill said that AMD initially left out a pair of instructions from its early AMD64 documentation, then decided later to add them back in. The two instructions are somewhat innocuous; the LAHF and SAHF instructions load and store status flags into a particular address. However, all of the other instructions listed in AMD’s published documents were later included in Intel’s chips. Halfhill said Intel engineers were unaware of the discrepancy until he contacted them.

“It’s impossible for this to be a coincidence; it’s just too similar,” Halfhill said, who added that a article describing the similarities will be published in The Microprocessor Report, which is published by In-Stat/MDR. Intel engineers did not contradict his conclusions when Halfhill submitted a copy of the article for a technical review, he said.

According to Intel, its 64-bit extensions are mostly compatible with AMD64. “Each company has a different microarchitecture,” George Alfs, an Intel spokesman, wrote in an email. “The real question is whether software ported on one processor will also run on the other. The answer in most cases is yes. As you remember from IDF, Steve Ballmer outlined the joint work both Microsoft and Intel have been doing for some time now on this technology.”

As the differences in the two architectures become more commonly known, Halfhill said that he believed a single version of a software program could be written to support both architectures, by avoiding all but the instructions used by both processor families.